While Xcel Energy and the federal government also are experimenting with ways to "store" wind power in the form of hydrogen, the Iowa Stored Energy Park would employ a far simpler strategy. Wind parks in Iowa, Minnesota and the Dakotas would ship energy over the power grid to a rural site outside Des Moines, about 230 miles south of the Twin Cities.

Three thousand feet below the surface outside Des Moines, a sandstone aquifer (caverns that now hold water) will be injected with pressurized air, with the air temporarily displacing some of the water. The electricity from wind turbines will power the compressors. A pipe will deliver underground air compressed to 900 to 1,000 pounds per square inch. The compression of millions of cubic feet of air will be scheduled for nights and weekends, when wind power often sells for next to nothing.

Wind parks pay for themselves when demand and electricity rates are higher -- during weekdays and on hot summer days. But when electricity is most needed, sometimes the wind isn't blowing.

Kent Holst, development director of the stored energy park, said the plan could transform the economics of wind power.

With the storage park option, the utility owners will be able to store and produce energy at a price equivalent to 6.5 cents per kilowatt hour, then sell the energy at peak times for 8 to 10 cents a kilowatt hour.